First Principles Study And Design Of Ohmic Contact Of GaN-based Light Emitting Diodes

Ni-assisted annealing?NA?experiment was proposed by Prof.Fengyi Jiang of Nanchang University?this achievement won the first prize for national technology invention in 2015?to solve the contradiction of the Ag-based Ohmic contact that has been unable to achieve high reflection and low barrier at the same time.The purpose of this article is to further explain this important experimental phenomenon in theory.Baesd on the density function theory,the first principles calculation was performed to find that the defects could reduce the barrer height at Ag?111?/GaN?0001?interface.The mechanism of Ohmic contact modulated by defects is revealed from the atomic and electronic scale.Moreover,a new method of using Cu as an assisted metal to realize a novel Ag-based Ohmic contact was proposed.General speaking,some up to date results are presented here:First principles calculations are carried out to establish the Ag?111?/GaN?0001?interface model,which agrees well with the experiment.The macroscopic averaging method is carried out to study the SBHs of defect-free and defective interfaces.The SBH of the defect-free interface is 2.221 eV,which is close to the SBH of 1.9 eV at Ag/p-GaN diode confirmed by I-V-T measurement.In the case of V_Gaa interface,the SBH is 0.857 eV,the Ni_Agg interface is observed a decreased SBH of 2.067 eV,the Ni_Ag+V_Gaa interface has the lowest SBH of 0.375 eV in all the interfaces.The calculated results indicate that the defects can reduce the SBH,which is in good agreement with the NA experiment.Using the first-principles method,through the analysis of the electronic structure of defect-free and defective Ag?111?/GaN?0001?interfaces,we found that charge accumulations around the interfacial defective regions and an unpinning of the Fermi level.Based on the effect of interfacial composition on SBH,the vertical LED reflectors such as Aluminum?Al?,Copper?Cu?,Gold?Au?,Platinum?Pt?,Palladium?Pd?and Titanium?Ti?are chosen to activate Ag-based Ohmic contact,respectively.We find that only the Cu_Agg interface has a relatively low SBH similar to that of the Ni_Agg interface.We innovatively proposed a Cu-assisted annealing experiment,which provides ideas and theoretical basis for achieving the high-quality Ag-based Ohmic contact.